The invention relates to video key border generators, and particularly to a border generator capable of adding full or drop shadow borders, or outlines, of selectively increased sizes, to key signals.
Video production switchers are employed as part of modern television production processes to provide video signal mixing and special effects techniques. These techniques, in turn, allow the transition between video information from various picture sources by processes known as "mixing" or "wiping", or are used to process various video information to form a composite picture by means of electronic "keying" operations. Typical of such switcher apparatus is the Ampex Series 4000 production switcher shown, for example, in the Ampex Catalog No. 1809376-01, November 1979.
In the course of performing the various mixing, wiping and/or keying processes, picture definition, i.e., transitions in the picture, must be clearly emphasized. This is particularly true when keying in captions and other graphics. The emphasized picture definition is effected by the symmetrical or unsymmetrical bordering of the caption, video information, etc., with selected brightness, or by coloring various portions of the picture as, for example, the caption characters.
To provide such bordering, or edge effects, the video signal covering the keying signal is generated via a corresponding portion of the keying circuit, such as conventionally found in the mix/effects unit of a switcher. Thus, the given border effect is accomplished by selectively widening the keying signal in the vertical direction by means of a delay of two horizontal lines using successive ultrasonic 1H delay lines, and in the horizontal direction by means of a delay of two picture elements or pixels. In the case where a full border is being generated, the insert video signal itself must be delayed by one-half of these values, In the vertical and horizontal directions, to provide a symmetrical border of a single line width about all sides of the video insert. It is also possible to key into the background image, the outlines produced from the difference between the enveloping signal and the keying signal, and to provide picture emphasis by colorizing as by a matte outline. For colorizing captions, etc., each mix/effects unit employs a color background generator whose signal is supplied to the keying stage as insert video.
Such conventional video border generator systems have the major disadvantage of being unable to increase the size, or change the configuration, of a full or drop shadow border, or outline.